The present invention relates generally to a system of transmitting power from a rotating shaft to at least one other rotating shaft, and to a chain for transmitting power between the shafts. The present invention is particularly directed to a system where sprockets of fixed diameter are mounted on the shafts, and the chain engages the teeth of the sprockets. However, the chain of the present invention may be used with various types of power transmission systems employing rotating shafts.
Power transmission chains are widely used in the automotive industry in automobile transmission systems as well as in engine timing drives. Engine timing systems conventionally include at least one driving sprocket located on the crankshaft and at least one driven sprocket located on a camshaft. Rotation of the crankshaft causes rotation of the camshaft through a chain. In automotive transmission systems, power transmission chains are used, for example, between a torque converter and the input to an automatic transmission. Power transmission chains are also used in transfer cases for four-wheel drive vehicles.
A number of different methods are employed to provide power transmission between rotating shafts. One such method involves a continuously variable transmission system (CVT). In contrast to a transmission system employing sprockets or gears which provide a discrete number of fixed transmission ratios, a CVT system provides any transmission ratio within an allowable range. In general, an endless belt provides power transmission between a drive shaft pulley and at least one driven shaft pulley. Each pulley comprises a pair of conical disks, or sheaves, with converging ends facing each other, so that a groove is formed between the conical disks, and the belt is positioned within the groove. In at least one pulley, one conical disk is axially moveable with respect to the other. Because the diameter of the conical disk varies along the axis of the disk, axial movement of the moveable disk changes the running diameter of the belt around the pulley. This change in the running diameter results in a change of the transmission ratio.
Typically, CVT belts comprise a number of endless metal bands, such as laminated metal strips formed in a loop. A plurality of transverse elements are positioned along the bands, with the bands received in slots in the transverse elements. The transverse elements are typically stamped metal plates arranged front to back around the loop of the endless carriers. The transverse elements typically have a generally trapezoidal shape, with at least two surfaces adapted to contact the sides of the pulleys, thereby providing power transmission between the belt and the pulleys. U.S. Pat. No. 4,894,049, which is incorporated herein by reference, discloses a typical CVT belt known in the art.
Another type of power transmission system employs a chain with links having inverted teeth, sometimes referred to as a silent chain, and at least one toothed sprocket on each rotating shaft. Power transmission between each sprocket and the chain, and consequently between one sprocket and another sprocket, is provided by the meshing of the sprocket teeth with the inverted teeth of the chain.
Inverted tooth chains are formed by an arrangement of link plates in lateral and longitudinal directions. The links are interlaced and joined by pins. A typical chain is composed of inner links, which contact the teeth of a sprocket to provide power transmission, and guide links, which do not provide power transmission. Guide links are employed to maintain the chain on the center of the sprocket when the chain is wound around the sprocket. A row of link plates, arranged in the lateral direction, typically has a number of inner links combined with guide links in the center or at both edges of the row. Each inner link plate typically comprises a body portion having a pair of apertures for receiving the pins, and at least one depending toe shaped to fit between the teeth of the sprocket and provide power transmission therewith. U.S. Pat. No. 5,347,581, which is incorporated herein by reference, shows an inverted tooth chain known in the art.
Inverted tooth chains and CVT belts each have certain disadvantages with respect to strength and durability. CVT belts typically have limited capacity when wrapped around pulleys of small diameter, because of the acute bending required of the metal bands. Inverted tooth chains, which articulate by the rotation of link plates about the pins, do not have this problem when employed with sprockets of small diameter. However, inverted tooth chains are susceptible to damage resulting from a large torque applied to one of the rotating shafts. Excessive torque applied to an inverted tooth chain may cause bending of the pins or failure of the link plates in the area around the pin apertures.
In contrast, excessive torque applied to a CVT belt is transmitted along the length of the belt by compression of the transverse elements against each other. Failure resulting from such torque only occurs if the torque is sufficient to cause deformation of the transverse elements or tensile failure from the bending of the CVT belt. Accordingly, CVT belts are generally less susceptible to failure from excessive torque when operated over a large diameter rotating member.
Accordingly, it is an object of the present invention to provide a power transmission system capable of withstanding high torques applied to the rotating members. It is another object of the present invention to provide a power transmission system having advantages of both CVT belts and silent chains. It is a further object of the present invention to provide a power transmission system having a chain of which absorbs torque by compression of its members which is suitable for use in a fixed ratio power transmission system. It is still another object of this invention to provide a power transmission system having a chain which absorbs torque by compression of its members which is adapted to operate with a toothed sprocket and to provide power transmission therewith. Other objects of the invention will be apparent to one skilled in the art.